This invention relates generally to key operated protective devices and especially to power control devices which can be employed to prevent the unauthorized use of machinery. More particularly, the present invention relates to key operable safety switches of the type used as safety guard switches.
While not limited thereto in its utility, the present invention is particularly well suited for use as a safety guard switch for electrically powered machinery. Such switches are known in the art as exemplified by the disclosures of German Patent 3,100,862 and published German Patent Applications Nos. 3,330,109, and 3,433,048.
Switches of the type shown in these German Patent and applications generally include an actuating member or key, a housing, a contact, a roller with roller parts and a contact carrier. In operation of this type of prior art safety switch, the actuating member is inserted through an opening in the housing to engage the roller parts and release the roller. Subsequent insertion of the actuating member rotates the roller thereby causing the contact carrier to be displaced, actuating the switch.
Current safety switches suffer from several problems. Typically, the actuating members supplied by the switch manufacturer are all identical to one another. Security is therefore compromised because the switch may be actuated by means of a readily available duplicate actuator. Attempts have been made to solve this problem. For example, an actuating member having a plurality of parts, which must be mounted jointly to perform their function, has been utilized. However, the parts may be mounted on a small board or the like, thereby providing a duplicate key. Another design utilizes an individually electronically coded actuating member in association with a safety switch equipped with an integral reading head and evaluation unit. This design requires larger switches and actuating members and can lead to problems with regard to locating the evaluation unit.